Preparation of vesiculated core/shell polymeric particles

Abstract

A process for the manufacture of core/shell polymer particles comprises forming a core particle containing acid functionality, a first shell around said core of a copolymer of a nonionic monoethylenically unsaturated aromatic monomer and a copolymerisable polar monomer in an amount of at least 15% by weight of the copolymer and having a solubility in water at 20° C. of at least 1% by weight and a second shell around said first shell of a polymer or copolymer of a nonionic monomer having a solubility in water at 20° C. of less than 1% by weight and swelling the particle with a non-volatile alkali to generate one or more vesicles. Preferably each shell contains a polymer or copolymer of styrene.

We claim: 
     
       1. A process for the manufacture of vesiculated core/shell particles comprising: forming an aqueous emulsion of at least one ethylenically unsaturated monomer with acid functionality, polymerising said unsaturated monomer to form core particles of polymer   forming an aqueous dispersion of said core particles and a monomer mixture of a nonionic monoethylenically unsaturated aromatic monomer and a copolymerisable polar monomer in an amount of at least 15 per cent by weight of the total weight of the monomer mixture and said copolymerisable polar monomer having a solubility in water at 20° C. of at least 1 per cent by weight   polymerising said monomer mixture to form a first shell on said core particles   adding to an aqueous dispersion of said core particles having a first shell a further nonionic monomer which has a solubility in water at 20° C. of less than 1 per cent by weight and polymerising said further monomer to form a second shell on the said particles, and   mixing the core/shell particles so obtained with a non-volatile inorganic base to swell the cores and generate therein one or more vesicles.   
     
     
       2. A process according to claim 1 in which the amount of said copolymerisable polar monomer is from 25% to 80%. 
     
     
       3. A process according to claim 1 in which the said polar monomer is selected from the group consisting of methyl methacrylate, acrylonitrile and methacrylamide. 
     
     
       4. A process according to claim 1 in which said nonionic monomer employed to form said first shell or said second shell is selected from the group consisting of styrene, alpha-methylstyrene, vinyl toluene, ring substituted derivatives of styrene, of alphamethylstyrene, and of vinyl toluene and mixtures thereof. 
     
     
       5. A process according to claim 1 in which the amount of said nonionic monomer used to form the first shell is greater than 25 per cent by weight of the total monomer mixture employed to form the first shell. 
     
     
       6. A process according to claim 1 in which the monomer mixture used to form the second shell is free of said copolymerisable polar monomer. 
     
     
       7. A process according to claim 1 in which said mixture of monomers used to form said first shell, or said second shell or both contains a soft monomer selected from the group consisting of butyl acrylate, ethyl acrylate, isobutyl acrylate, ethyl hexyl acrylate, butadiene, isoprene, lauryl methacrylate, a long chain esters of acrylic acid, a long chain ester of methacrylic acid, dibutyl maleate and mixtures thereof. 
     
     
       8. A process according to claim 1 in which said core is formed by polymerising an acidic monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, aconitic acid, maleic acid, maleic acid anhydride, fumaric acid and crotonic acid. 
     
     
       9. A process according to claim 1 in which the core is a copolymer of an unsaturated monomer selected from the group consisting of methyl methacrylate, styrene, vinyl toluene, alpha methyl styrene, ethylene, vinyl acetate, vinyl chloride, acrylonitrile, acrylamide, methacrylamide, alkyl esters of methacrylic acid and of acrylic acid and of vinyl alcohol, and alkenyl esters of methacrylic acid and of acrylic acid and of vinyl alcohol. 
     
     
       10. A process according to claim 1 in which the core contains at least 10 per cent by weight of said monomer containing acid functionality. 
     
     
       11. A process according to claim 1 in which the said base is an alkali metal hydroxide. 
     
     
       12. A process according to claim 1 in which the said base is an alkali metal bicarbonate. 
     
     
       13. A core/shell polymer particle comprising: a core containing acid functionality of a polymer or copolymer of an ethylenically unsaturated monomer   a first shell around said core formed of a copolymer of a nonionic monoethylenically unsaturated aromatic monomer and a polar monomer in an amount of at least 15 per cent by weight of said copolymer and said polar monomer having a solubility in water at 20° C. of at least 1 per cent by weight,   and a second shell of a polymer or copolymer of a nonionic monomer having a solubility in water of less than 1 per cent by weight, and   said core/shell particles having at least one vesicule formed by reaction with a non-volatile inorganic base.